author | Sverre Rabbelier <srabbelier@gmail.com> |
Sun, 02 Nov 2008 17:26:06 +0000 | |
changeset 429 | e50e18936f06 |
parent 204 | 7075c27170f2 |
permissions | -rw-r--r-- |
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# |
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# Copyright (c) 2008 Andreas Blixt <andreas@blixt.org> |
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# Project homepage: <http://code.google.com/p/blixt/> |
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# |
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# License: MIT license <http://www.opensource.org/licenses/mit-license.php> |
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# |
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"""Data-related Google App Engine extensions. |
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""" |
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from google.appengine.ext import db |
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import sys |
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# Add ModelWithFieldAttributes *before* PolyModel, so that everything does |
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# not become a "ModelWithFieldAttributes" in the Datastore. |
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from soc.models import base |
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class Error(Exception): |
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"""Base of all exceptions in the blixt.data module.""" |
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pass |
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class PolyModel(base.ModelWithFieldAttributes): |
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"""An extension to Google App Engine models that improves the support for |
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inheritance. |
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Any models extending a model that extends PolyModel will be stored in the |
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datastore as the same kind as the model that extends PolyModel, but with |
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their additional properties. When they are retrieved from the datastore, |
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they will be loaded as the appropiate model class. |
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The difference from the Model class is that queries will include models that |
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inherit from the model being queried. |
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""" |
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inheritance_line = db.StringListProperty() |
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def __init__(self, parent = None, key_name = None, _app = None, **kwds): |
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"""Creates a new instance of this polymorphic model. |
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Args: |
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parent: Parent instance for this instance or None, indicating a top- |
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level instance. |
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key_name: Name for new model instance. |
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_app: Intentionally undocumented. |
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args: Keyword arguments mapping to properties of model. |
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""" |
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if self.__class__ == PolyModel or not isinstance(self, PolyModel): |
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raise Error('Instances of PolyModel must be created through a ' |
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'subclass of PolyModel.') |
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line = [] |
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for c in self.__class__.__mro__: |
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if c == PolyModel: |
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self.__class__._kind = p |
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break |
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line.append('%s.%s' % (c.__module__, c.__name__)) |
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p = c |
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kwds['inheritance_line'] = line |
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super(PolyModel, self).__init__(parent = parent, key_name = key_name, |
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_app = _app, **kwds) |
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@classmethod |
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def _kind_type(cls): |
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"""Gets the class highest in the model inheritance hierarchy (the class |
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that will be used as the datastore kind.) |
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""" |
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p = cls |
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for c in cls.__mro__: |
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# The meta-class 'PropertiedClass' calls kind() which leads here. |
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# The variable 'PolyModel' is not assigned until after the meta- |
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# class has finished setting up the class. Therefore, a string |
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# comparison is used instead of a value comparison. |
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if c.__name__ == 'PolyModel': break |
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p = c |
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return p |
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@classmethod |
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def all(cls): |
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"""Returns a query over all instances of this model, as well as the |
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instances of any descendant models, from the datastore. |
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Returns: |
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Query that will retrieve all instances from entity collection. |
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""" |
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qry = super(PolyModel, cls).all() |
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if cls != cls._kind_type(): |
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full_name = '%s.%s' % (cls.__module__, cls.__name__) |
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qry.filter('inheritance_line =', full_name) |
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return qry |
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@classmethod |
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def from_entity(cls, entity): |
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"""Converts the entity representation of this model to an instance. |
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Converts datastore.Entity instance to an instance of the appropiate |
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class, which can be cls or any descendant thereof. |
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Args: |
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entity: Entity loaded directly from datastore. |
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Raises: |
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KindError when cls is incorrect model for entity. |
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""" |
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if entity.has_key('inheritance_line'): |
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mod_name, cls_name = entity['inheritance_line'][0].rsplit('.', 1) |
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__import__(mod_name) |
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cls = getattr(sys.modules[mod_name], cls_name) |
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return super(PolyModel, cls).from_entity(entity) |
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@classmethod |
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def kind(cls): |
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"""Returns the datastore kind we use for this model. |
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Todd Larsen <tlarsen@google.com>
parents:
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This is the name of the class that is highest up in the inheritance |
187d45783300
Add the third-party PolyModel class. This class supports inheritance in
Todd Larsen <tlarsen@google.com>
parents:
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121 |
hierarchy of this model. |
187d45783300
Add the third-party PolyModel class. This class supports inheritance in
Todd Larsen <tlarsen@google.com>
parents:
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changeset
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122 |
""" |
187d45783300
Add the third-party PolyModel class. This class supports inheritance in
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
123 |
return cls._kind_type().__name__ |
187d45783300
Add the third-party PolyModel class. This class supports inheritance in
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
124 |